Acoustic panel for receiving, emitting or absorbing sounds

ABSTRACT

An acoustic panel, designed to emit, receive, or absorb sound, includes two walls ( 12, 14 ) that are arranged opposite one another and delimiting an inner space ( 16 ), whereby the inner space ( 16 ) includes at least 50% air and is equipped with at least one cavity ( 16 ), at least one element ( 20 ) that can become deformed, elements ( 22 ) for exerting a force on the at least one deformation element ( 20 ), and elements ( 24 ) for connecting the at least one element to a surface ( 26 ) of one of the walls ( 12, 14 ), with the at least one deformation element ( 20 ), connecting elements ( 24 ) and surface ( 26 ) delimiting a chamber.

This invention relates to an acoustic panel, designed to emit and to receive sound or to absorb sound.

In general, acoustic panel is defined as either an acoustic chamber that comprises a loudspeaker and that provides sound from an electric signal, or a facing, such as a wall facing, designed to passively reduce ambient noise.

Such an acoustic chamber can come in various forms and at various costs, according to the quality of sound that is emitted by the loudspeaker. In particular, for obtaining a top-quality acoustic chamber, systems of vibratory membranes have been developed that consist of composite materials, which have a high production cost, both because of their arrangement and the type of the materials used, and their technology, as based on the use of electrostatic chambers.

On the other hand, a sound absorption facing is generally used in the reduction of noise in a building or a vehicle.

There is therefore need for an acoustic panel that makes possible several operating modes, i.e., able to emit and to receive sound, or to absorb sound.

It is the purpose of this invention to eliminate the above-mentioned drawbacks by proposing an acoustic panel structure that makes possible a “triad” operation—either sound absorber, or sound receiver, or sound generator—and, in this sound emission mode, constitutes a loudspeaker of high acoustic quality while being of simple and economical design.

For this purpose, the invention relates to an acoustic panel, designed to emit, receive, or absorb sound, characterized in that it comprises two walls that are arranged opposite one another and delimiting an inner space, whereby said inner space comprises at least 50% air and is equipped with at least one cavity, at least one element that can become deformed, means for exerting a force on said at least one deformation element, and means for connecting said at least one element to a surface of one of said walls, with said at least one deformation element, connecting means and surface delimiting a chamber.

The invention also relates to a device for generating sound waves, characterized in that it integrates an acoustic panel as described above and comprises at least one piezoelectric element, and in that it comprises means for supplying at least one piezoelectric element with voltage.

The invention will now be described in more detail with reference to the accompanying figures provided only by way of example and in which:

FIG. 1 is a diagrammatic cutaway view of an acoustic panel in accordance with the invention,

FIG. 2 is a representation of the acoustic panel according to several shape variants, and

FIG. 3 is a representation of the evolution of the frequency response of the acoustic panel (expressed in terms of dB) of FIG. 1 in loudspeaker mode, based on the frequency (expressed in terms of Hz).

In the figures, an acoustic panel—designed to emit, receive or absorb sound, comprising two walls 12, 14, arranged opposite one another and delimiting an inner space 16—is referenced as 10. The inner space 16 comprises at least 50% air and is equipped with at least one cavity 18. The acoustic panel 10 also comprises at least one element 20 that can become deformed, means 22 for exerting a force on said deformation element, and connecting means 24 of said element to an outside surface 26 of the wall 12. A chamber 28 is delimited by the at least one deformation element 20, the connecting means 24, and the surface 26 of the wall 12.

According to one embodiment, the at least one deformation element 20 is a membrane 30 of an electromechanical transduction element. The electromechanical transduction element is preferably a piezoelectric element, but any converter of mechanical energy into electrical energy and vice versa is also suitable for the implementation of this invention. This piezoelectric element is advantageously tuned to operate in a frequency range of between 20 Hz and 25,000 Hz.

According to the embodiment that can be seen in FIG. 1, the connecting means 24 of the membrane 30 to the surface 26 come in the form of a peripheral edge 34 of the membrane 30 and are made integral, for example, by bonding to the outer surface 26. According to one embodiment, the means 22 exert a counter-reaction force F and are arranged in contact with the membrane 30 from an outer side 31 a, opposite to the chamber 28, or, in contrast, from an inner side 31 b, in the chamber 28.

According to a variant, not shown, the chamber 28 can be arranged in the inner space 16, and the connecting means 24 connect the membrane 30 to the inner surface 33 of the wall 12. The means 22, integral with the membrane 30, are also arranged in the inner space 16.

The means 22 can come in various forms. They can involve, as shown in FIG. 1, at least one mass 38, in which case the force F that is exerted is equal to mγ, where γ is the acceleration of the mass. They can also come as a mass-spring system that is tuned to the low frequencies and that makes it possible to reduce the runaway of the piezoelectric element in response to a strong electric pulse. Actually, at low frequencies, a large portion of the wall 12 radiates mechanical energy and is vibrating. The presence of the mass then makes it possible to amplify and to tune the amplitude of the vibrations of the panel 10.

According to one variant, the mass 38 is a metal ball, connected to the center of the membrane 30 by means of a glue, preferably of the elastomer type such as neoprene or butyl. The presence of the glue between the mass 38 and the membrane 30 means that the connection between the mass 38 and the membrane 30 is elastic and dampened. The support between the mass 38 and the membrane 30 being specific and central, it allows a controlled deformation of the membrane 30, which contributes to a high sound quality of the acoustic panel.

According to another variant, the membrane 30 carries two masses 38 that are arranged in such a way that the deformation effects are symmetrical, ensuring a high quality of the sound emitted by the acoustic panel.

The means 22 can also come in the form of a viscoelastic element or a fairly rigid spring linked to a heavier element.

The walls 12 and 14 preferably consist of a material that is light and rigid, such as plastic, polycarbonate, cardboard or else expanded polystyrene. The advantage of these types of materials is that they are economical to use in comparison in particular with composite materials that are generally used for a top-quality loudspeaker. The acoustic panel 10 can be monolithic and consist of, for example, a cardboard sheet or a section of expanded polystyrene. It is also possible that the walls 12 and 14 form two layers of a trilayer made by the two walls 12, 14 and the inner space 16 filled with an absorbent material, such as foam.

The acoustic panel can be filled at least partially by an absorbent material, such as foam, which then provides to the inner space 20 a multitude of cavities 18, as shown in a diagram in FIG. 1. The filling material is advantageously light and comprises cells, such as alveolar cardboard.

The acoustic panel 10 can assume various shapes shown in FIG. 2. It can be a parallelepipedic panel, as for the panels 10-1 and 10-2, or curved, as for the panels 10-3 and 10-4, or else cylindrical, as for the panel 10-5. The acoustic panel 10 can also be a sphere. The panel 10 can comprise a recess, even with a dimension that is greater than 20% of the total surface area of the acoustic panel. The acoustic panel can be extremely flat, as shown in 10-1, or, in contrast, very thick; see panel 10-5.

It is noted that the invention is not limited to the embodiment of FIG. 1, and, in particular, the number of piezoelectric elements and membranes 30 as well as their distribution in the panel 10 depend on numerous parameters such as the type, dimensions, and the number of sheets of material, and the presence or absence of cavities.

In particular, when the panel 10 comprises several piezoelectric elements, the excitation of a maximum of suitable modes of the vibratory wall is preferred, over that which is known in the state of the art in the design of a loudspeaker. This excitation of suitable modes makes it possible to obtain low frequencies, reduces the possibility of inter-acoustic wave interference that degrades the sound quality of the acoustic panel, and makes it possible to excite other suitable modes that would not be excited by a single piezoelectric element.

It is noted that the various piezoelectric elements that are used are not necessarily in phase. For example, a spatialization effect can be obtained using two phase-shifted piezoelectrics.

It is also noted that when several piezoelectric elements are mounted according to a determined network, it is possible to focus the emitted acoustic waves.

The acoustic panel 10 can operate according to three different modes, either by emitting, or by receiving sound, or by absorbing sound.

The first operating mode is the acoustic absorption mode according to which the absorbent material of the acoustic panel makes it possible to reduce the sound level. This operating mode can be totally passive and permanent, or else active by emitting sound in phase opposition with the one arriving above.

The second operating mode is acoustically active, making it possible to generate sound emissions. In this operating mode, the acoustic panel is used as a loudspeaker: a sound signal is generated by a computer, an MP3 key, or a Walkman, for example, and then it is sent digitally by network or in analog form to the piezoelectric element after being pre-amplified. The piezoelectric element converts this electrical energy into mechanical energy, which causes the membrane 30 to vibrate, and the vibrations are transmitted to the wall 12 by the air of the chamber 28 and then to the entire panel 10 by means of the at least one inner cavity 18, which becomes resonant, and by means of the connecting means 24 that carry the vibrations of the membrane 30 to the wall 12. The presence of the mass 38 makes it possible to amplify and to tune the amplitude of the vibrations. Acoustic waves are then emitted.

The piezoelectric element is supplied with a voltage supply, for example at ±20 V, because of the high impedance of the piezoelectrics that are used.

Thus, according to the acoustic emission operating mode, it is possible, in particular, to emit masking noise, ambient sound, or to create a musical atmosphere or to broadcast information.

The operating mode corresponds to that of a loudspeaker whose acoustic characteristics are particularly high-performing, as can be seen in FIG. 3. The curve in FIG. 3 is obtained without active or passive filtering. It thus is noted that in the absence of any filtering, the passband at −6 dB extends over a wide frequency band, from 100 Hz to 20,000 Hz, ensuring a very high sound quality of the panel 10.

The third operating mode is that of an acoustically active receiver. Actually, the ambient noise causes the panel 10 to vibrate, and it is possible to collect a signal by the piezoelectric element. This signal is very weak, but it can in turn be amplified by an integrated or offset amplifier. In this case, it is possible to ensure the surveillance of an unoccupied site—the detection of intrusions in closed sites, for example.

The invention also relates to a device for generating sound waves, characterized in that it integrates at least one acoustic panel 10 that is equipped with at least one piezoelectric element and in that it comprises means for supplying at least one piezoelectric element with voltage.

The acoustic panel according to this invention has a simple and economical design, in particular due to the use of cardboard or expanded polystyrene, while exhibiting noteworthy acoustic properties. In addition, it can have a thickness of only some millimeters and is thereby suitable for numerous applications. It can be, for example, integrated with furniture, in particular design furniture, such as a dresser or a lampshade. 

1. Acoustic panel, designed to emit, receive, or absorb sound, characterized in that it comprises two walls (12, 14) that are arranged opposite one another and delimiting an inner space (16), whereby said inner space (16) comprises at least 50% air and is equipped with at least one cavity (16), at least one element (20) that can become deformed, comprising a membrane (30) of an electromechanical transduction element, means (22) for exerting a force on said at least one deformation element (20), and means (24) for connecting said at least one element to a surface (26) of one of said walls (12, 14), with said at least one deformation element (20), connecting means (24) and surface (26) delimiting a chamber (28).
 2. Acoustic panel according to claim 1, wherein the electromechanical transduction element is a piezoelectric element that is tuned to frequencies of between 20 Hz and 25,000 Hz.
 3. Acoustic panel according to claim 1, wherein the walls basically consist of a material that is selected from among cardboard, polystyrene, plastic or polycarbonate.
 4. Acoustic panel according to claim 1, wherein the means (22) for exerting a force comprise at least one mass (38) that is connected to the deformation element (20).
 5. Acoustic panel according to claim 4, wherein the at least one mass (38) is a sphere that is glued to the center of the membrane (30) of the electromechanical transduction element.
 6. Acoustic panel according to claim 1, wherein the inner space (18) is at least partially filled with an absorbent material such as foam.
 7. Acoustic panel according to claim 2, wherein it comprises two piezoelectric elements that are regulated for being phase-shifted in such a way as to induce a spatialization effect.
 8. Device for generating sound waves, wherein it integrates an acoustic panel according to claim 2 and wherein it comprises means for supplying at least one piezoelectric element with voltage. 